This invention relates to dust recovery in iron manufacture and more particularly to a method and apparatus for separating zinc type material from iron material in such dust and removing the zinc type material, with the iron material being recycled into the manufacturing process.
In order to maintain good working conditions and prevent environmental pollution, in iron manufacturing furnaces such as blast furnaces, converters and electric furnaces, the dusts discharged from these furnaces are forcibly collected so as to avoid pollution of the air. Further, for the purpose of more effectively utilizing resources, iron-containing components are purified and recycled into the iron manufacturing furnaces, for example, after pelletization. These dust removing and recycling techniques are now broadly employed in the art of iron manufacture.
Dust collected in the above recycle process contain Zn, ZnO, Pb and the like (called "zinc type metals and compounds" in the instant specification and claims) in addition to Fe.sub.2 O.sub.3 and like iron compounds.
Accordingly, when these collected dusts are recycled repeatedly into iron manufacturing furnaces, such zinc type metals and compounds are accumulated and adhere to furnace walls and flues to cause clogging in furnace bricks thereby reducing the operation efficiency drastically. Moreover, there is the danger that these accumulated zinc type metals and compounds will deposit on the refractory materials of the furnace, thereby shortening the effective life of the furnace. In addition to these shortcomings, the accumulation of such zinc type material on the furnace tends to lower the grade of the raw steel produced.
As means for overcoming these defects and disadvantages, a method has been proposed in which recovered dusts are dipped in a dissolution tank and decomposed in several stages by chemically dissolving means such as a leaching process. However, this method has the disadvantages that the equipment involved is complicated, the operating cost is high, a considerable space is required and the operating maintenance requires very high technical capability.
Application of flotation dressing means to recovered dusts can also be employed, but conditions for operation in a high magnetic field in a magnetic dressing machine are very critical and this method does not lend itself for use in a practical operating situation.